Testing system for four-wire circuits



C. S. .DEMAREST. TESTING svsrsm roa FOUR-WIRE cmcuns.

APPLICATION FILED JULY 24 I920 1,394,190, Patented Oct. 18, 1921. 4SHEETS-SHEET l- I INVENTOR v afianamsl ATTORNEY C. S. DEMAREST. TESTINGSYSTEM FOR FOUR-WIRE CIRCUITS. APPLICATION- FILED my 24, I920.

Patented Oct. 18, 1921.

. 4 SHEETS-SHEET 2- INVENTOR 6: J: fiend/at BY ATTORNEY C. S. DEMAREST.

TESTING SYSTEM FOR FOUR-WIRE CIRCUITS. APPLICATION FILED JULY 24, 1920.

1,394,190, Patented 061:. 18, 1921.

4 SHEETSSHEET 3.

INVENTOR 653911022216 BY ATTORNEY 0. s. DEMAREST. TESTING SYSTEM FORFOUR-WIRE CIRCUITS. APPLICATION FILED JULY 24; I920.

Patented Oct. 18, 1921.

4 SHEETS-SHET 4.

INVENTOR 63 Jim;

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ATTORNEY UNITED STATES,

PATENT OFFICE.

CHARLES S. DEMAREST, OF RIDGEWOOD, NEW JERSEY, ASSIGNOR TO AMERICANTELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TESTING SYSTEM FOR FOUR-WIRE CIRCUITS.

Specification of Letters Patent.

Original application filed February 24, 1919, Serial No. 278,945.Divided and this application filed July 24, 1920. Serial No. 398,657.

To all whom it may concern:

Be it known that I, CHARLES S. DEMAREST, residing at Ridgewood, in thecounty of Bergen and Stateof New Jersey, have invented certainImprovements in Testing Systems for Four-Wire Circuits, of which thefollowing is a specification.

This invention relates to telephone transmission systems and moreparticularly to means for controlling the connection of telephonerepeaters to a four-wire telephone transmission circuit, and for testingthe efliciency of such type of circuit.

This application is a division of my copending application, Serial No.278,945, filed February 24, 1919.

Heretofore it has been customary to connect the repeaters into thefour-wire repeater circuit, and to maintain such connection permanently,regardless of the nature of the circuit that may be connected with eachend of the said four-wire circuit. The telephone repeaters connectedwith a four-wire circuit are usually designed and operated to give anamplification that will compensate notv only for the loss in thefour-wire circuit itself, but also for the losses in the telephone trunklines that may ordinarily be connected with the said four wire circuit.lVhen such a circuit is completely connected from subscriber tosubscriber, the repeater is balanced and will operate satisfactorily,that is, without singing. It has been found that whenever an operatorconnects her telephone set with such circuit for the purpose ofsupervising such connection, an unbalanced condition is created and therepeaters begin to sing, thereby impairing the transmission over thecircuit.

It is the object of this invention to provide a testing circuitthefunction of which is to determine whether the repeaters are operatingproperly so as to produce the desired transmission gain.

This invention will'be better understood from the following description,when read in connection with the attached drawing of which Figure 1shows a cord circuit at, for example, a toll oflice to connect theincoming trunk circuit with the four-wire repeater trunk shown in Fig.2, which for purpose of description, is assumed to extend between twotoll oflices; Fig. 3 shows a cord circuit at the other of said tollofiices to connect said repeater trunk with circuits of the type withwhlch the repeater circuit is designed to cooperate. Fig. 4 shows atesting circuit by means of which the repeaters shown in Fig. 2 may betested. The complete circuit may be clearly seen by arranging all theFigs. 1, 2 and 3 so that the bottom edge of Figs. 2 and 8 coinciderespectively with the top edge of Figs. 1 and 2. Fig. 4 should bearranged symmetrically below Fig. 2.

Fig. 1 shows a cord circuit at the toll board E terminating in a plug Padapted to beinserted in the jack J 8 of the testing circult shown inFig. 4 and also in a plug P, adapted forinsertion in either jack J 4 orjack J of the toll circuit shown in Fig. 2.

Fig. 2 shows a four-wire repeater trunk circuit extending between twotoll ofiices, designated-E and F, and terminating at each of theseoffices in two jacks. The four-wire circuit is of the usual type, havingtwo twowire branches which are electrically related by means of thehybrid repeating coils X and Y. Associated with coil X are two networksN and N the former. being adapted to balance the circuit connected withjack J and the latter being designed to control the transmission gainwhen the repeater is connected through the jack J with a circuit havinga lower transmission equivalent than that connectedwith the jack J Whena circuit is connected with jack J both networks are connected into therepeater circuit. In a similar manner coil Y has associated with it twonetworks N and N N being adapted to balance the circuit connected withjack J and N, functioning as a gain control network for a circuitconnected with jack J Each group of jacks at either end of the four-wirecircuit has associated with it a group of relays controlled by thecircuits connected with said jacks and adapted to control relays 25 and26 of the repeater circuit which, in turn control the connection of therepeaters to the branches of the fourwire circuit, and the connection ofthe heater batteries with the filaments.

Fig. 3 shows a cord circuit located at the toll ofiice F terminating intwo plugs P and P P being adapted for insertion in jacks J and J of thefour-wire trunk circuit and plug 1? being adapted for insertion injack J9 of the testing circuit shown in Fig. 4.

'ofiice F and likewise plugs Fig. 4 shows the repeater testing equipmentwhich is preferably though not necessarily located inithe same office inwhich the repeatershown in F ig. 2 is located and is connected by meansor ring-down trunks 67 and 68 with the switchboards at the toll oflicesE and F terminating therein in jacks J and J respectively;

known type, has the same transmission equivalent as the four-wirecircuit has when the repeaters are disconnected. A swltch 74 is providedfor connecting the oscillator 70 with either end of the repeater circuitor'of the artificial line 72. A switch 75 is provided to connect theoscillator and the receiver alternately with the transmission circuitand with the artificial line;

In order to'test the repeater, plug P is inserted in j ack J and plug Pin jack J Plug P is inserted in jack J 8 at toll oflice E and plug'P isinserted in iack J, at toll 4 and P are inserted in jacks J and 5respectively. Relay 12 of the'cord circuit at ofiice E and relay 37 or"the cord circuit at ofiice F will be operated,and if thekeys in bothcord circuits are normal the repeaters 59 and 60 will be energized inthe manner shown clearly in my'copending application, Serial No.278,945, filed February 24, 1919. If key 74 of the testing circuit isoperated in the left hand direction an alternating electromotive forcewill be applied over contacts of keys 74 and f 7 6, tip and ringcontacts of plug P and jack J trunk 67, over the tip and ring conductorsof the cord circuit at oifice E,through branch 77 of the four-wirerepeater circuit including the repeater 59, over the con- 7 ductors ofthe cord circuit at ofiice F andthe conductors of trunk 68, tip and ringcontacts of jack J and plug P right hand normals contacts of switches 76and 74,

through receiver shunt 73 to the receiver 71.

Switch 75 is'now operated, thereby causing the operation of relays 79and 80, which disconnects the" source of tone 70 and the receiver' 71from the trunk circuits 67 and 68, respectively, and connects saidsource of tone toone end ofthe artificial line 72, and the receiver 71to the other end of said artificial line. o.

e The receiver shunt 73 is gradually varied o until the volume of tonereceived in the receiver 71; when the receiver is connected across theartificial line IS the same as when and the plug it is connected acrossthe trunk leading to one end of the four-wire repeater circuit.

If the switch 74' is thrown "in. the right hand direction the source 'ofalternating of jack J and plug P left hand contacts of switches 76 and74, receiver shunt 73 to receiver 71. By operating switch 75 in themanner heretofore described thevibrator 70 and thereceiver and receivershunt are alternately connected with the four-wire circuit and with theartificial line, and shunt 73 is varied until the volume of tone in thereceiver 71' when the receiver is connected with the artificial line isthe same as when connected with the four-wire repeater circuit. Thereading upon the scale of the receiver shunt represents the transmissiongain due 'to the presence of repeater 60 in the circuit.

By insertin the plug. P, in the jack J 5 in the jack J it; will be notedthat there has been included in the four-wire transmission circuit thenetworks N and N and consequently the artificial line 72must have thesame impedance as the four-wire circuit including the said networks buthaving the repeaters disconnected. If, however, the said plugs'areinserted in jacks J and J respectively, the networks are not included inthe said four-wire circuit (as has been shown in my copendingapplication, Serial No. 278,945,- filed' February 24, 1919) andconsequently the artificial line 72 must be adjustedso as to have thesame characteristic impedance as the four-wire circuit without thenetworks N and N and with the repeaters disconnected;

From the foregoing description'of the apparatus in which this inventionis embodied and of its mode of operation, it will be seen that thisinvention provides a simple and eificient'method' for'determining the improvement in transmission due to the connection of the repeaters 1n thefour-wlre transmlsslon clrcult. Although th1s invenelectromotive forcewill be applied to the tion is shown as embodied in the single form, itis apparent that itis capable of em bodiment in other andvaried formswithout departing from the spirit and scope of the appended claims. 7 7

'l/Vhat is claimedis: V

1. In a telephone system, the combination ofa four-wire repeatertrunkcircuit,-having telephonic repeaters associated therewith butnormally disconnected therefrom, a testing circuit comprising anartificial line having a transmission equivalent equal to that of therepeater trunk circuit when the said repeaters are disconnected, andlink circuits for connecting said repeater circuit with said testingcircuit, the said testing circuit being adapted to apply an alternatingelectromoti-ve force or" telephonic frequency alternately to one end ofsaid circuit and to one end of said artificial line, a receiver and ameasuring device adapted to be alternately connected with the other endof said repeater trunk circuit and with said artificial line, wherebythe tones received in said re ceiver may be compared as to magnitude.

2. In a telephone system, the combination with a four-wire transmissioncircuit having repeaters associated therewith but normally disconnectedtherefrom, a testing circuit, link circuits having a plurality of keysassociated therewith arranged to connect the said four-wire circuitswith the said testing circuit, and switching means for effectivelyconnecting the said repeaters with the said four-wire circuit when thesaid link circuits are connected with their respective associatedcircuits and all but one of said keys are in their unoperated positions.

3. In a telephone system, the combination with a four-wire repeatercircuit of testing trunk circuits, link circuits for connecting each endof the said repeater circuit with its corresponding testing trunkcircuit, an artificial line having the same transmission efiiciency asthe said four-wire circuit when the repeaters are disconnectedtherefrom, a source of testing potential, a measuring device and meansto connect both the said source and the said device alternately with thesaid testing trunks and with the said artificial line.

, 4. In a telephone system, the combination with a four-wire repeatercircuit having a plurality of repeaters associated therewith butnormally disconnected therefrom, of a gain testing circuit and aplurality of link circuits for connecting the said repeater circuit withthe said testing circuit, the link circuits having means associatedtherewith for controlling the connection of the said repeaters with thesaid four-wire circuit.

5. In a telephone system, the combination with a four-wire repeatercircuit having line balancing networks and gain control networksassoeiated with each end thereof, the said four-wire circuit terminatingin a plurality of jacks at each end, of a testing circuit having anartificial line of adjustable impedance associated therewith, linkcircuits adapted to connect the said testing circuit with the saidfour-wire circuit, and to control the connection of the said gaincontrol networks with the said four-wire circuit.

6. In a telephone system, the combination with a four-wire repeatercircuit having a plurality of repeaters associated therewith butnormally disconnected therefrom and also line balancing networks andgain control networks associated therewith, of a testing circuit havingan artificial line whose impedance may be Varied, and also a source ofelectromotive force and a gain measuring device associated therewith,and link circuits for connecting the said four-wire circuit with thesaid testing circuit and adapted to control the connection of the saidrepeaters and also of the said gain control networks with the saidfour-wire circuit.

In testimony whereof, I have signed my name to this specification thistwenty-first day of July, 1920.

CHARLES S. DEMAREST.

